Effect of urban emissions on the horizontal distribution of metal concentration in sediments in the vicinity of Asian large cities

Abstract: Metal contents of sediments in Manila Bay – Laguna Lake watershed in the Philippines were measured and detailed horizontal distribution was obtained. The distribution of zinc and lead concentration in Manila Bay clearly shows the effect of anthropogenic contamination and it was explained by the diffusion of lead and zinc rich anthropogenic particles discharged from Pasig River. The sediments in Laguna Lake were mostly natural particulate matters from surrounding mountains and they contained 20 mgPb/kg and 100 mgZn/kg, while the sediment taken at the heavily polluted branches of the Pasig River contained as high as 88 mgPb/kg and 310 mgZn/kg. The lead and zinc concentrations in the sediments of Manila Bay – Laguna Lake watershed were compared with those in the mouth of the Tama River, Tokyo, where the faster deposition of coarser natural origin particles and slower deposition of lead and zinc rich anthropogenic particles determined the sediment concentration. The comparison was also made with Hanoi City, Vietnam. In spite of the difference in time when leaded gasoline was prohibited, the difference in the lead concentrations of roadside deposits and sediments was not obvious in the vicinity of these three target cities. This is probably due to dilution by a large amount of suspended solids conveyed by the Pasig River in the case of the Philippines. Storm water runoff containing roadside deposits and discharge of untreated wastewater were identified as factors increasing zinc and lead concentrations of sediments in receiving waters based on the measurements on roadside deposits and the estimation of the contribution of untreated wastewater.

Effect of urban emissions on the horizontal distribution of metal concentration in sediments in the vicinity of Asian large cities

T Urase1*, K Nadaoka2, H Yagi2, T Iwasa1, Y Suzuki1

F Siringan3, T P Garcia4, T T Thao5

1: Dept of Civil Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8552 Japan

*: Corresponding author turase@fluid.cv.titech.ac.jp, +81-3-5734-3548

2: Dept of Mechanical and Environmental Informatics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8552 Japan

3: National Institute of Geological Sciences, University of the Philippines, 1101 Diliman, Quezon City, Philippines

4: Dept Civil Engineering, College of Engineering, Technological University of the Philippines, Manila, Philippines

5: Department of Analytical Chemistry, Hanoi University of Science, 19- LeThanh Tong street, Hanoi, Vietnam

Abstract:

Metal contents of sediments in Manila Bay – Laguna Lake watershed in the Philippines were measured and detailed horizontal distribution was obtained The distribution of zinc and lead concentration in Manila Bay clearly shows the effect of anthropogenic contamination and it was explained by the diffusion of lead and zinc rich anthropogenic particles discharged from Pasig River The sediments in Laguna Lake were mostly natural particulate matters from surrounding mountains and they contained 20 mgPb/kg and 100 mgZn/kg, while the sediment taken at the heavily polluted branches of the Pasig River contained as high as 88 mgPb/kg and 310 mgZn/kg The lead and zinc concentrations in the sediments of Manila Bay – Laguna Lake watershed were compared with those in the mouth of the Tama River, Tokyo, where the faster deposition of coarser natural origin particles and slower deposition of lead and zinc rich anthropogenic particles determined the sediment concentration The comparison was also made with Hanoi City, Vietnam In spite of the difference in time when leaded gasoline was prohibited, the difference in the lead concentrations of roadside deposits and sediments was not obvious in the vicinity of these three target cities This is probably due to dilution by a large amount of suspended solids conveyed by the Pasig River in the case of the Philippines Storm water runoff containing roadside deposits and discharge of untreated wastewater were identified as factors increasing zinc and lead concentrations of sediments in receiving waters based on the measurements on roadside deposits and the estimation of the contribution of untreated wastewater

Keywords: Laguna Lake; lead; Manila Bay; sediment; wastewater; zinc

Introduction

Asian cities generally have large populations Human activities and their impacts on natural environments are concentrated in the vicinity of urban regions High precipitation in Asian regions results in erosion of land and induces urban runoff during wet weather days A large amount of particulate matters having natural and anthropogenic sources flows into receiving watersheds Incomplete sewer problems such as low coverage and combined sewer overflows (CSOs) arise more seriously in Asian regions compared with those of other relatively dry regions

Among various pollutants associated with particulate matters, heavy metals especially lead and zinc are paid attention in this study because they may be toxic to aquatic animals and because their distributions in environment are strongly affected by diffuse anthropogenic sources (Callender et al.,

2000) After the occurrence of hurricane Katrina in the United States, the contamination of soil, caused by lead as high as 400 mgPb/kg, was identified as one of the environmental concerns after the flood (Presley et al., 2006) Although there are many studies showing anthropogenic pollution

by lead and zinc in Asian regions (Zhang et al., 2001), detailed spatial distribution of these metals

in the Manila Bay – Laguna Lake watershed has not been presented The effect of urban emissions

on the sediment quality has to be discussed

In this study, detailed horizontal distribution of the metals in sediments in the Manila Bay – Laguna Lake watershed in the Philippines was obtained and the effect of anthropogenic contamination by untreated wastewater and urban storm water on the distribution of metals is discussed The obtained metal concentrations in the sediments in the Philippines were compared with those in other Asian countries using the same method and instruments The measurement of metal content in roadside deposits, which are possible origins of sediments, is also reported

Materials and Methods

Sediment samples

In the Philippines, 36 sediment samples from Manila Bay, 9 samples from Laguna Lake, 7 samples from Pasig River, which connects Manila Bay to Laguna Lake, and at its branches, were taken in

2002 A grab sampler that can collect surface sediments with approximate depth of 5 cm corresponding to a few-year deposition in the case of Manila Bay was used in the sampling of sediments Eight river sediment samples were taken at the tidal zone around the mouth of the Tama river, Tokyo in 2002 Five sediment samples were collected in Hanoi city in 2005 The sampling locations in Hanoi were To-Lich River, Lu River and Kin-Nguu River, which receives untreated wastewater and urban runoff without having their origins outside Hanoi Inner District Maps of the sampling locations are shown in the results section of this paper

Roadside deposit samples

Roadside deposits are possible sources of sediment contamination in receiving waters In order to investigate the contribution of roadside deposits to the sediment metal concentration increase, seven roadside deposit samples were collected in Manila, Philippines from 2002 to 2003 A total of 83 roadside deposit samples were collected in Meguro - Ohta - Setagaya, Tokyo, Japan and 81 roadside deposit samples were collected around all inner districts in Hanoi city, Vietnam during dry weather days in 2005 in order to compare them to the metal content in the Philippines The road surface of sampling sites was asphalt or concrete Roadside deposits were collected by sweeping the road surface using a brush

Surface water samples

To investigate the lead concentration in the water phase associated with suspended matters, surface water samples were taken from Laguna Lake, Pasig River and at its branches, San Juan River and Marikina River in 2002

Chemical analysis of sediment samples and roadside deposit samples

The sediment samples were dried in an oven at 110oC for 24 hours The dried samples were mixed thoroughly to achieve homogeneity and sieved through a 2-mm plastic sieve to remove gravel-sized materials, leaves and other particles prior to analyses of metal concentration and ignition loss A laser particle analyzer LIST-100 was used for the measurement of the particle size of Manila Bay samples, while another laser particle analyzer SALAD-3000, Shimadzu was used for the measurement of other samples

Heavy metals were extracted using the aqua regia digestion method Approximately 0.5g of dry sediment samples was acid-digested using 2 ml of concentrated nitric acid and 4 ml of concentrated hydrochloric acid in a glass vessel covered with watch glass The samples were heated at 120oC for

2 hours Two milliliters of 1:1 HNO3 was added to the residue and the mixture was filtered using a Whatman 5B glass fiber filter The solution was then diluted to a final volume of 100 mL This method gives strong acid extractable fraction which can be regarded as pseudo total content of metals (Morillo et al., 2004) (Tessier et al., 1979) After the extraction, the concentration of Cr, Cu,

Fe, Mn, Ni, Pb, Zn determined using a ICP-AES instrument (Shimadzu ICP-7000 model)

Accuracy of the measurement was confirmed through the analysis of Laguna Lake samples, as shown in the result section of the paper In addition, the accuracy was also confirmed through the monitoring results obtained by the Ministry of Environment (MOE), Japan (2004), for sediments including those Tokyo Bay with the same pretreatment technique as was used in this survey The monitoring results for Tokyo Bay by MOE showed 47mgPb/kg for the sediment with mean particle size of 3.9um, and 39 mgPb/kg for the sediment with 10um particle size, which is consistent with this study

Chemical analysis of surface water samples

Both total lead concentration and dissolved lead concentration were measured for surface water samples Nitric acid digestion followed by filtration with a Whatman 5C glass fiber filter was employed for the determination of total lead content before the instrumental analysis On the other hand, the concentration of dissolved fraction was determined for the filtrate samples with the same type glass fiber filter before nitric acid digestion ICP-MS model SPQ-9000 (Seiko Instruments) was used for the determination of lead concentration Chloride ion concentrations and suspended solid concentrations (SS) were also measured for the surface water samples

Results

Sediment samples taken in the Philippines

The iron contents in the samples of sediments in the Philippines were distributed in a narrow range

of 3.6% - 4.5% for Manila Bay samples, 5.4% - 5.8% for Laguna Lake samples and 4.7% - 6.3% for the Pasig River samples as shown in Figure 1 (a) The particle size measurement showed that soil particles in the river sediment samples were coarser than those in the Laguna Lake samples and Manila Bay samples However, all the samples consisted mostly of silt and clay as shown in Figure

1 (b) with the mean volume of around 10 micrometer and with lower than 17% sand content

Figure 1(c), 1(d), 1(e) and 1(f) show the horizontal distribution of copper, nickel, lead and zinc concentrations in the sediments The distribution of copper and that of nickel made it difficult to simply correlate their concentrations with the human activities in Metro Manila Lower concentrations of lead and zinc were observed for the samples taken from the western part of Manila Bay and Laguna Lake except for those taken from the northwest part of the lake The sediments originating from natural erosion and flow into the lake from surrounding mountains were considered to contain 20 mgPb/kg and 110 mgZn/kg based on the uniform distribution of these metals in the sediments of the lake The higher concentration in the northwest part of the lake is probably due to reverse flow of the polluted Pasig River in dry season

Manila Bay

Laguna Lake

65 68 63 59

93 88 75 62 94 86

72 81 96

64 101 62 66 8087 94

99 80 63 63 58 72 10998

1016376 47 42

127 121 132 138

124 121 79 119

133(P1) 114(P2) 114(SJ) 167(P3) 76(P4) 60(P5) 128(MK)

(c) Cu (mg / kg dry solid)

Manila Bay

17 18 15 20

30 28 23 14 24 21

15 15 17

15 33 14 13 26 13 20

15 26 17 18 15 11 7 11

17 1723 13 10

10 11 12 10

14 10 9 9

25(P1) 26(P2) 15(SJ) 17(P3) 21(P4) 16(P5) 25(MK)

(d) Ni (mg / kg dry solid)

Manila Bay

4.0 4.33.7 4.5

4.1 4.5 4.6 3.8 4.44.4

4.3 4.44.8 3.6 4.3 3.8 3.74.3 4.0 4.4

3.74.3 4.0 4.2 4.04.45.0 4.2

4.03.94.3 4.04.4

3.8 4.3 4.5 5.8

5.4 5.4 5.5 5.8

5.7 5.6 8.8 5.6

5.9(P1) 5.9(P2) 5.8(SJ) 5.5(P3) 5.6(P4) 4.7(P5) 6.3(MK)

(a) Fe (% dry solid)

Central Manila Manila Bay

9 10 9 9

9 10 9 10 9 8

12 9 8

8 11 11 9 10 9 8

9 12 12 10 12 11 12 11

8 1012 20 17

9 7 10 11

9 12 16 11

16(P1) 14(P2) 10(SJ) 11(P3) 16(P4) 12(P5) 16(MK)

(b) Volume mean dia (µm)

Central Manila

Laguna Lake

Manila Bay

Laguna Lake

10 11 12 12

12 16 18 14 22 38

16 23 41

13 18 12 13 2327 41

15 15 15 16 17 20 24 27

15 1418 16 16

27 20 22 22

21 19 16 18

71(P1) 51(P2) 88(SJ) 29(P3) 18(P4) 13(P5) 23(MK)

(e) Pb (mg / kg dry solid)

Manila Bay

91 99 89 94

134124113106 148173 105153220

92 147 89 87 110198 218

11511490 88 81 84 95 128

1209210468 63

106 102 107 106

110 90 119 91

311(P1) 239(P2) 195(SJ) 186(P3) 148(P4) 113(P5) 209(MK)

(f) Zn (mg / kg dry solid)

Laguna Lake

N

Manila Bay

Laguna Lake

65 68 63 59

93 88 75 62 94 86

72 81 96

64 101 62 66 8087 94

99 80 63 63 58 72 10998

1016376 47 42

127 121 132 138

124 121 79 119

133(P1) 114(P2) 114(SJ) 167(P3) 76(P4) 60(P5) 128(MK)

(c) Cu (mg / kg dry solid)

Manila Bay

17 18 15 20

30 28 23 14 24 21

15 15 17

15 33 14 13 26 13 20

15 26 17 18 15 11 7 11

17 1723 13 10

10 11 12 10

14 10 9 9

25(P1) 26(P2) 15(SJ) 17(P3) 21(P4) 16(P5) 25(MK)

(d) Ni (mg / kg dry solid)

Manila Bay

4.0 4.33.7 4.5

4.1 4.5 4.6 3.8 4.44.4

4.3 4.44.8 3.6 4.3 3.8 3.74.3 4.0 4.4

3.74.3 4.0 4.2 4.04.45.0 4.2

4.03.94.3 4.04.4

3.8 4.3 4.5 5.8

5.4 5.4 5.5 5.8

5.7 5.6 8.8 5.6

5.9(P1) 5.9(P2) 5.8(SJ) 5.5(P3) 5.6(P4) 4.7(P5) 6.3(MK)

(a) Fe (% dry solid)

Central Manila Manila Bay

9 10 9 9

9 10 9 10 9 8

12 9 8

8 11 11 9 10 9 8

9 12 12 10 12 11 12 11

8 1012 20 17

9 7 10 11

9 12 16 11

16(P1) 14(P2) 10(SJ) 11(P3) 16(P4) 12(P5) 16(MK)

(b) Volume mean dia (µm)

Central Manila

Laguna Lake

Manila Bay

Laguna Lake

10 11 12 12

12 16 18 14 22 38

16 23 41

13 18 12 13 2327 41

15 15 15 16 17 20 24 27

15 1418 16 16

27 20 22 22

21 19 16 18

71(P1) 51(P2) 88(SJ) 29(P3) 18(P4) 13(P5) 23(MK)

(e) Pb (mg / kg dry solid)

Manila Bay

91 99 89 94

134124113106 148173 105153220

92 147 89 87 110198 218

11511490 88 81 84 95 128

1209210468 63

106 102 107 106

110 90 119 91

311(P1) 239(P2) 195(SJ) 186(P3) 148(P4) 113(P5) 209(MK)

(f) Zn (mg / kg dry solid)

Laguna Lake N

Figure 1 Concentration of iron (a), copper (c), nickel(d), lead (e) and zinc (f) and mean particulate size (b) in the sediments taken from Manila Bay, Pasig River and Laguna Lake, in the Philippines

Higher concentration was observed for samples taken in the eastern side of Manila Bay The concentration profiles in the sea sediments show the decrease in lead and zinc concentrations in the sediments with the increase in the distance between the river mouth and the sampling location This concentration profile, as also reported by Prudente et al (1994), suggests that the sources of a certain ratio of lead and zinc are anthropogenic and they were continuously discharged from Pasig River, which collects most of the emission loads from Manila central area The lower concentration

in the northwest part of the bay is due to dilution of polluted solids by a large amount of Pinatubo solids carried by rivers flowing from the north of the bay Figure 1 also shows that the samples

taken from downstream of Pasig River (Stations P1, P2) and San Juan River (Station SJ), which collects untreated wastewater and urban storm water runoff, contained high concentrations of lead and zinc

Table 1 summarizes the results of all the target metals in this study Concentration of metals like copper and nickel other than lead and zinc were distributed in narrow ranges and were not sensitive for the pollutants discharged from Pasig River based on their spatial distribution Except for zinc, almost no difference was observed between our results on Laguna Lake and previous measurements

by Hallare et al., (2005), which suggests that the measurements in this study are accurate and reliable and sediments in this lake are quite stable and uniform The difference in the data for zinc is due to some mistakes in Hallare’s results taking into account the very small concentration of their reported values for zinc

Table 1 Summary of the metal contents of sediments in the Philippines (mg/kg)

for the eastern part

Pasig River and its branches

Laguna Lake except for the northwest part

2005

*: one abnormal sample was excluded

**: some mistakes might be associated

Sediment samples in Tama River, Tokyo, Japan and in Hanoi, Vietnam

In order to compare the metal concentrations of sediments in the Philippines with those in other countries, an additional sampling was carried out in Tokyo and in Vietnam Figure 2 shows the case

in the tidal zone at the mouth of Tama River, Tokyo The sediment samples taken from the first, second and fourth locations counting from the mouth of the river consisted mostly of silt and clay with less than 20% sand content However, the third sample contained 64% of sand and other upstream samples mostly consisted more than 97% of sand Lead and zinc concentrations in Figure

2 show higher concentrations for fine sediments in the downstream and smaller concentrations for coarse sediments in the upstream This concentration profile can be explained by a combination of less polluted sandy particles carried by Tama River in the events of heavy rain from mountain area upstream and finer metal rich particles which can be settled down in Tokyo Bay where flow is slower

Lead concentration of 20 mg/kg for the less polluted coarser sediments in Tama River, Tokyo is

almost the same as the concentration we observed for the Laguna Lake fine sediments In the case

of zinc, 70 mgZn/kg of the coarse samples in Tama River was a little lower than 100 mgZn/kg in the Laguna Lake possibly due to difference in particle size or difference in natural soil property

In Vietnam, the sediment samples in streams inside Hanoi city contained 37 – 107 mgPb/kg and 240-460 mgZn/kg as shown in Figure 3 The concentration ranges in the sediments of the streams in Hanoi city were in the same ranges as were observed for severely polluted San Juan River in the Philippines and the finer sediments of Tama River, Tokyo

Pb 18; Zn 72

Pb 23; Zn 86

Pb 37; Zn 94

Pb 28; Zn 92

Pb 57;

Zn 146

Pb 75;

Zn 178

Pb; Zn (mg / kg dry solid) Sand 50% or above Silt sand clay 50% or above

Tokyo DID

Kawasaki DID

Tama River

Pb 62; Zn 151

Pb 26; Zn 95

Pb 18; Zn 72

Pb 23; Zn 86

Pb 37; Zn 94

Pb 28; Zn 92

Pb 57;

Zn 146

Pb 75;

Zn 178

Pb; Zn (mg / kg dry solid) Sand 50% or above Silt sand clay 50% or above

Tokyo DID

Kawasaki DID

Tama River

Pb 62; Zn 151

Pb 26; Zn 95

Figure 2 Concentrations of lead (a) and zinc (b) of the sediments taken from

the tidal zone of the mouth of Tama River, Tokyo, Japan

West Lake

R

ed R iver

Pb 107; Zn 454

Pb 41; Zn 241

Pb 37; Zn 440

Pb 46; Zn 251

Pb 84; Zn 461

Hanoi Central West Lake

R

ed R iver

Pb 107; Zn 454

Pb 41; Zn 241

Pb 37; Zn 440

Pb 46; Zn 251

Pb 84; Zn 461

Hanoi Central

Figure 3 Concentrations of lead and zinc in sediments at small streams of

Hanoi City, Vietnam

Roadside deposits

Roadside deposit is one of the possible origins of polluted sediments in receiving waters The metal concentrations in the roadside deposit samples taken at Meguro - Ohta – Setagaya, Tokyo, Hanoi inner districts, and Manila were compared in Table 2 Though the deviation is quite large, especially for the samples in the Philippines due to small number of samples, lead and zinc concentrations were higher in roadside deposits than those in sediments in the receiving watersheds in the case of Tokyo and Philippines Effect of heavy traffic was observed by dividing Tokyo samples into minor street samples and major street samples In the case of Vietnam, the concentrations of the roadside deposit samples were lower than those of sediments probably because of incomplete road pavement and frequent construction works, which diluted traffic origin particles Experimental results in Tokyo and in the Philippines are in the same level compared with a report by Lee et al (2005) showing 190 mg Pb/kg for mean concentration of roadside sediments based on a large number of samples taken in Korea In the case of Tokyo and in the Philippines, urban runoff from roads on rainy days contributes to the increase in metal concentration in the sediments of receiving watersheds based on the relatively higher concentrations of roadside deposits compared with those

of sediments

Table 2 Concentration of acid-soluble heavy metals in the roadside deposit samples

Particulate matters in surface water

Surface water was sampled in the Philippines and its total metal concentration, dissolved metal concentration, and suspended solid concentration were measured to calculate the metal concentration associated with suspended sediments The samples were taken when no seawater intrusion was found for the sampling locations based on the completely fresh water level of chloride ion content smaller than 110mg/L in the samples

Table 3 gives the results of metal concentration of the suspended sediments Based on the particle weight, the sample taken at San Juan River, which is a severely polluted branch of the Pasig River, contained high concentration of lead (as high as 200 mg Pb/kgSS) corresponding to the highest concentration of the sediment samples in this study Similarly, the Laguna Lake samples contained

20 mgPb/kgSS as was found for the sediment samples at the lake Pasig River conveys as much as

80 mg/L of suspended solids with the same metal content as was observed for Laguna Lake fine sediments

Table 3 Concentration of lead in surface waters and its recalculated concentration based on the weight of suspended solids

Lead (Pb)

(ug/L)

C dis

(ug/L)

C par

(mg/kg)

Note:

C SS : Suspended solid concentration in water

C tot : Total Pb concentration in water

C dis : Dissolved Pb concentration in water

C par : Suspended Pb concentration in solids C par =(C tot - C dis ) / C SS

Discussion

Most gasoline were unleaded in 1980 in Japan, in 2001 in the Philippines and in 2001 in Vietnam The core sample analysis of the sediment in Tokyo Bay shows the peak concentration for the layer deposited in early 1970s and gradual decrease in late 1970s corresponding to the countermeasures against leaded gasoline(Matsumoto, 1983) In spite of the difference in time when leaded gasoline was prohibited, the difference in concentration of the roadside deposits and the sediments is not obvious among these three cities One of the reasons for small difference in lead concentration in sediments is the dilution through a large amount of suspended solids supplied by the Pasig River as shown in the Philippines As high as 80 mg/L suspended solids with lower lead content diluted the anthropogenic contamination

This study shows that the sediments of streams that receive untreated wastewater contained higher concentrations of lead and zinc The data on the metal concentration of wastewater in the Philippines is not available In the case of other countries, Karvelas et al.(2003) reports that in Greece, more than 90% of zinc and lead contained in raw wastewater were associated with suspended solids and their concentrations based on suspended solid weight were 56 mgPb/kgSS and 710 mgZn/kgSS, respectively Asai et al (2005) calculated the mean concentration of raw wastewater influent to wastewater treatment plants in Japan, giving 37 mgPb/kgSS and 1,400 mgZn/kgSS as averaged values of a large number of samples by assuming 100% particlulate association of the metals Sörme et al.(2002) identified domestic, construction and car related sources as the main sources of zinc in wastewater in Sweden, while they failed to identify the source of lead, suggesting the contributions of traffic related sources and street dusts accumulated

in the past when leaded gasoline was dominantly used These reported zinc concentrations are much higher than the sediment concentration in this study, suggesting that the untreated wastewater is one

of the important factors contributing to the elevated zinc concentration in the sediments, though

several transport and adsorption processes have to be considered to link between untreated wastewater and sediments

In the case of lead, other sources than domestic wastewater are necessary considering the lead content in wastewater This study implies that storm water runoff carrying roadside deposits is another source of the elevated lead content in the sediments, though several transport and adsorption processes have to be considered to link sediments and roadside deposits Furumai et al (2002) reported that the concentration of heavy metals contained in an express way effluent in Switzerland, was 180 mgPb/kgSS, which is much higher than the sediment concentration The management of urban storm water is essential to decrease the metal concentration in sediment, considering that the area of road is more than 15% in most larger cities and that the roof runoff may have similar contamination

Conclusion

Metal contents in sediments in Manila Bay – Laguna Lake watershed in the Philippines were measured and detailed horizontal distribution was obtained The distribution of zinc and lead concentrations in Manila Bay clearly shows the effect of anthropogenic contamination and it was explained by the diffusion of lead and zinc rich anthropogenic particles discharged from Pasig River The sediments in Laguna Lake were mostly natural particulate matters from surrounding mountains and they contained 20 mgPb/kg and 100 mgZn/kg, while the sediment taken at the heavily polluted branches of the Pasig river contained as high as 88 mgPb/kg and 310 mgZn/kg The lead and zinc concentrations in the sediments of Manila Bay – Laguna Lake watershed were compared with those

in the mouth of the Tama River, Tokyo, where the faster deposition of coarser natural origin particles and slower deposition of lead and zinc rich anthropogenic particles determined the sediment concentration The comparison was also made with Hanoi city, Vietnam In spite of the difference in the time when leaded gasoline was prohibited, the difference in the lead concentration

of roadside deposits and sediments was not obvious in the vicinity of these three target cities probably due to dilution by a large amount of suspended solids conveyed by the Pasig River in the case of the Philippines Storm water runoff containing roadside deposits and discharge of untreated wastewater were identified as factors increasing zinc and lead concentration in the sediments in receiving waters judging from the measurements on roadside deposits and the estimation of the contribution of untreated wastewater

Acknowledgement

The authors give sincere thanks to Y Nakagawa at port and airport research institute, MLIT for the measurement of particle sizes for the Manila Bay samples The survey in the Philippines was supported by the core university program by Japan Society for the Promotion of Science between Tokyo Institute of Technology and the University of the Philippines The survey in Vietnam was supported by UNESCO international research course for environment

References